1. Field of the Invention
The invention relates in general to a wireless communication technology, and more particularly, to a method and a device for signal processing.
2. Description of the Related Art
The Long-Term Evolution (LTE) standard demands a transmitter to have different transmission requirements for different frequency bands. For example, for the frequency band 13 (Band 13), as the Band 13 is located only 2 MHz from a public safety band, the LTE standard requires a transmitter operating on the Band 13 to significantly reduce the transmission power in order to guarantee that the leaked power posed on the public safety band is within a very small range, e.g., a range within −57 dBm. However, reducing the transmission power noticeably affects the transmission performance of the transmitter.
In a transmission path of a transmitter, processes including baseband filtering, frequency mixing and driving amplification are performed to obtain a radio-frequency (RF) signal for transmission. However, due to a nonlinear distortion of the transmission path, harmonic signals occur near the RF signal to be transmitted. For example, the harmonic signals may be intermodulation 3 (IM3) signals, also referred to as 4FMOS signals, which are generated by the nonlinear distortion of the transmission path. The frequency of such signals exactly falls within the range of the public safety band. Due to the presence of the 4FMOS signals, a transmitter operating on the Band 13 barely achieves the requirements of the LTE standard.
Further, the generation of the harmonic signals consumes the power of a transmitter, lowering not only the power of RF signal transmitted but also the transmission performance of the transmitter.
The U.S. Patent Publication No. 20110306300A1 discloses a method for harmonic suppression and/or rejection. The above method is a harmonic elimination method base on analog nonlinearity. To also achieve preferred suppression effects, during the process for eliminating harmonic signals, a calibration operation needs to be performed. However, such analog operation has complicated implementation and is thus not practical.
Therefore, there is a need for a simple method for compensating the nonlinear distortion of a transmission path of a transmitter and for enhancing the transmission performance of the transmitter.